The invention relates to a device designed for lubrication of a bearing block with a ball joint.
More precisely, the invention relates to a device to automatically lubricate a ball joint in a closed circuit, during rotation movements of a hinge pin supported by the bearing block.
The invention is particularly but not exclusively applicable to bearing blocks supporting landing gear on the structure of an aircraft. In this case, lubrication is done during landing gear extension and retraction movements.
An aircraft retractable landing gear comprises several parts, such as the main fitting of the landing gear and the strut, that are equipped with a number of hinge pins fixed in rotation to the aircraft structure, in order to define the same number of rotation axes (for example two axes of rotation in the transverse direction relative to the aircraft). These axes of rotation define a down and up movement for the landing gear, in the case of the aircraft landing gear.
The connection between the different hinge pins in the landing gear and the aircraft structure is frequently defined by the use of bearing blocks fitted with ball joints. These ball joints enable the different hinge pins in the landing gear to add pivoting movements with respect to the aircraft structure, in addition to rotation movements allowed by the different axes of rotation. These pivoting means, also called xe2x80x9cswiveling phenomenonxe2x80x9d, cause slight rotations of the landing gear about two other axes of rotation that define an orthogonal system with the axis of rotation considered.
The swiveling phenomenon occurs for example when deformations of the aircraft structure take place. These deformations take place particularly during maneuvers on the ground (taxiing) or during some flight phases during which high stresses may be applied to the said structure.
The ball joints in these ball joint bearing blocks usually comprise a ball capable of pivoting into a cage. One procedure for manufacturing such a ball joint is described in document U.S. Pat. No. 1,693,748; The cage in this ball joint is made from a single piece, one end of which is machined to the required shape before the ball is inserted into the said cage. An annular protuberance is formed on the outside of the cage, at its second end. This second end of the cage is then deformed by inserting the said cage by force fitting it into its support. This has the effect of creating the final shape of the cage and enclosing the ball inside it.
This process becomes difficult to implement when the dimensions of the ball joint are large. In this case, the cage may be composed of two secondary half cages inserted in a cylindrical primary cage to enable assembly of the ball.
The above mentioned deformations of the aircraft structure may cause relative movements between the ball and the cage, corresponding to the swiveling phenomenon already mentioned, and translation displacements, or even slight rotations, at the hinge pin at the inside of the ball, if the said hinge pin is not fixed inside the ball.
These displacements under load have the effect of applying friction forces on the bearing block ball joints. These friction forces are particularly high if the loads producing the deformations are high and if the friction coefficient between the surfaces is bad. From this point of view, it is known that the coefficient of friction varies particularly as a function of the materials present and the lubrication.
Friction forces can create a resisting torque between the ball and the cage that can prevent the ball joints from fulfilling their function entirely to compensate for deformations. Friction forces may also make it impossible for the hinge pin to rotate within the ball under satisfactory conditions, when a torque and/or axial forces are applied to the said hinge pin.
These phenomena can sometimes cause damage to landing gear hinge pins, for example due to occurrence of local overstresses at the ends of the bearing block, due to bending of the hinge pin that causes a longitudinal misalignment of the hinge pin in the bearing block.
These phenomena may also cause rotation of the secondary half cages in the primary cage. This rotation causes misalignment of the lubrication orifices and lubrication grooves. The result is that grease can no longer be replaced in the said grooves, which can have the consequence of causing damage to insufficiently lubricated surfaces, in other words damage to the ball joint.
Finally, the phenomena caused by friction forces may also cause damage to the fittings forming the structural parts of the landing gear, when torques and parasite forces have been applied to them.
These various problems are particularly sensitive when deformations of the aircraft structure are large. Frequently, these deformations themselves increase with the flexibility of the aircraft, which is usually higher for large aircraft. In this case, the above mentioned problems related to friction forces need special attention.
One known technique of reducing friction forces consists of lubricating firstly the contact surfaces between the ball and the bearing block cage in which this ball fits, and secondly contact surfaces between the hinge pin of the landing gear and the reaming made in the ball into which this hinge pin fits; This lubrication is done by injecting grease between the said contact surfaces during maintenance operations.
More precisely, surfaces to be lubricated are usually provided with grooves or slots in which grease can circulate and can therefore be distributed over these surfaces. Grease is injected under pressure using a pump, through grease nipples connected to the grooves. Old grease is expelled from the grooves through appropriate orifices.
Maintenance operations are usually carried out approximately every 500 hours of operation of the landing gear, corresponding to intervals of about 4 months for a medium haul aircraft, under normal operating conditions.
This technique for the renewal of grease used to lubricate ball joint bearing blocks in aircraft landing gear introduces several problems.
Thus, we have seen that the grease is only renewed periodically after a number of operations of the landing gear between two maintenance operations. Therefore, the grease ages, which is usually accompanied by a deterioration to its lubrication properties. This degradation is worsened by pollution, temperature and pressure variations, etc.
Furthermore, if the quantity of new grease injected during a maintenance operation is insufficient, it is possible that not all old grease will be expelled from the lubricated surfaces. In this case, lubrication of the said surfaces will not be as good because the old grease will remain mixed with new grease. This situation is particularly likely, since old grease can sometime block up the grooves, preventing it from being entirely replaced by new grease.
Furthermore, after a number of operations of the landing gear, some of the grease is expelled on the edges of the lubricated surfaces. Therefore, lubrication of these surfaces is not as good due to the lack of grease.
Specifically, the purpose of the invention is a device for lubrication of a ball joint bearing block, with an innovative design such that it renews grease between the contact surfaces at every rotation of the hinge pin, in a closed circuit, particularly to limit aging of the grease, the risk of no grease being present and the risk of the grooves being blocked by old grease, in order to improve the lubrication quality and reduce grease consumption.
According to the invention, this result is achieved by means of a device for lubrication of a ball joint bearing block comprising a pivot hinge pin, the device comprising at least one lubrication groove for the ball joint bearing block, characterized in that the device also comprises a lubricant reservoir connected through a closed circuit to the groove, pumping means designed to circulate the lubricant in the circuit between the reservoir and the groove, and means of activating the pumping means under the effect of a rotation movement of the pivot hinge pin.
This device renews the lubricant, in other words usually grease, between the lubricated surfaces of the bearing block during each rotation of the pivot hinge pin. Therefore, depending on the capacity of the reservoir, grease is therefore used much less frequently than if a lubrication device according to prior art is used. This limits aging and consequently improves the lubrication quality.
Furthermore, since grease frequently circulates in the grooves, the obstruction of grooves by old grease is much less probable than when a device according to prior art is used.
Furthermore, since the pumping means inject grease into the grooves during each rotation of the pivot hinge pin, there is no longer any risk of poor lubrication of contact surfaces due to lack of grease, as is possible with a device according to prior art.
Furthermore, the device according to the invention is capable of renewing grease in a closed circuit. Therefore, grease consumption is limited to the renewal of grease during periodic maintenance operations.
In one preferred embodiment of the invention, the device comprises at least two lubrication grooves and means of cyclically distributing the lubricant to each of the said grooves, during successive rotation movements of the pivot hinge pin.
Advantageously, the pumping units comprise a piston free to move in a given direction inside the lubricant reservoir, in order to divide the reservoir into a number of variable volume chambers.
In this case, a first of the said chambers is advantageously connected to a first end of a first groove through a first safety valve, the second chamber is connected to the second end of the first groove through a second safety valve provided with non-return means, the second chamber is connected to a first end of a second groove through a third safety valve and the first chamber is connected to the second end of the second groove through a fourth safety valve fitted with non-return means.
In general, the ball joint bearing block comprises a ball joint cage, a ball joint ball mounted in the ball joint cage and the said pivot hinge pin which passes through a reaming formed in the ball joint ball. The first groove is then formed between the ball joint cage and the ball joint ball and the second groove is formed between the ball joint ball and the pivot hinge pin.
Preferably, first leak tightness means are provided between the ball joint cage and the ball joint ball, on each side of the first groove, and second leak tightness means are provided between the ball joint ball and the pivot hinge pin, on each side of the second groove.
To enable replacement of grease during maintenance operations, a passage for injection of new grease advantageously joins a first grease nipple to the first end of the first groove and a passage for expulsion of old lubricant connects the first chamber to a second grease nipple.
In one advantageous variant embodiment, the two chambers with variable volume are connected to a compensation chamber that contains lubricant kept under pressure by appropriate means, such as a second piston. This variant can reduce the dimensions or use seals with lower sealing characteristics.
In the preferred embodiment of the invention, the lubricant reservoir and the mobile piston are preferably housed inside the pivot hinge pin, so that its center line is coincident with the center line of the pivot hinge pin.
In the latter case, the means of actuating the pumping means advantageously include a connecting rod, the first end of which is hinged on the piston at a location eccentric from the said common center line, and a second end of which is hinged on a structure fixed to the bearing block cage at a location that is also offset from the said common center line.
According to one preferred non-limitative application of the invention, the pivot hinge pin forms part of an aircraft landing gear.
Successive operations to retract and extend the landing gear then cause successive rotations of the pivot hinge pin in one direction or the other, with the effect of injecting lubricant alternately into the first groove and the second groove.